The present invention relates to an information processing apparatus, such as an optical disk apparatus and the like, in which a laser beam is directed toward the optical disk, and variations in the refractive index of a recording film or the like are used to record and reproduce the information.
An analog signal reproduced from the optical disk is converted into a binary signal represented by "1" and "0". This operation is called a binarization. Binarization can be accomplished by the well-known slice level method at the well-known differentiated reproduced signal method.
A binary digital signal is input to a PLL (Phase Locked Loop) circuit, and a data sequence synchronized to a reproduced clock can be obtained. This data sequence is called channel data.
After binarization, the binary signal is passed through the PLL circuit, and channel data comprising "1"s and "0"s are obtained. The obtained channel data is, for example, a 2-7 modulated code sequence. The 2-7 modulation is a kind of RLL (Run Length Limited) code, and since the minimum run is "2" and the maximum run thereof is "7", the modulation is called 2-7 modulation. In general, the term "run" means a series of bits with the same value ("0" or "1") or a continuous bit length, where, without specific notes, it is assumed that the continuous number of "0" bits is called the run.
In 2-7 modulation, the series of "1" bits does not exist, and the continuous number of "0" bits ranges from "2" to "7". The RLL code has a finite maximum inversion distance. Although, the data sequence which a user wants to record in the optical disk via a drive apparatus (henceforth, referred to as user data, and this data is original data before the modulation) may have many "1" bits or "0" bits in a row, 2-7 modulation is carried out. As a result it is possible to obtain a code in which a "1" bit is necessarily generated within a constant period.
Since in the PLL circuit, phases are compared by the timing of a transition from "0" to "1" or from "1" to "0" of the signal after binarization (henceforth, referred to as a binary signal), 2-7 modulation is used. As a result an interval of phase comparison can be necessarily within the constant period. The channel data is input to a demodulator, and the channel data is inverse-converted into the user data.
The data is recorded in the optical disk in a unit called a sector. A size of the sector is, for example, "512B", "1KB", "2KB", or the like. "B" denotes a byte, and in general, one byte is equal to "8" bits. This sector includes, for example, a header portion formed by an embossed pit, user data recorded by emitting the laser beam when the data is recorded, a VFO, a sector number, a synchronous code, a CRC code, an ECC code or the like, and 2-7 modulation is carried out so that, for example, the information is recorded by using a record between marks.
The synchronous code is a particular data sequence in which "1B" is added to user data having "15B (bytes)", a bit shift or the like is corrected by the synchronous code, and transmission of an error is prevented. The CRC code is used for discriminating whether the error exists in the read user data or not, etc., and for example, the CRC code of "4B" is added to user data of "512B".
The ECC code is the code for detecting the error position and for correcting the error, and for example, the ECC code of "80B" is added to user data of "512B". The sector number is recorded in the portion called a pointer region, and for example, sector number data of "4B" is added to user data of "512B". The user data is input to an optical disk drive apparatus from an information input terminal, etc., via an SCSI bus or the like.
The SCSI (Small Computer System Interface) is a peripheral device interface of a small-sized computer, and the SCSI is used for the optical disk drive apparatus, a CD-ROM, a hard disk, an image scanner, or the like. The obtained user data is stored in a DRAM (Dynamic Random Access Memory) or the like by a sector unit.
The user data is interleaved, and a burst error is converted into a random error and a short byte error. For example, when the user data is "512B" per "1" sector, a pointer (4B), the CRC (4B) and the ECC (80B) are added to the user data of "512B". The resultant data of "600B" is arranged in a matrix (120.times.5). The matrix comprises five columns having "120B", and each column comprises the data of "104B" (either the user data, the pointer, or the CRC) and the ECC code of "16B ". As the ECC code, for example, an LDC (Long Distance Code) is used.
The LDC is the code having a long minimum distance and a high correction ability. The LDC is one proposed standardization of the optical disk. In this case, the LDC detects and corrects the error in one column comprising "120B". In case of "non-erasure error", a correction up to "8B" can be carried out.
An erasure error means the error whose position is known, but whose pattern (value) is not known.
If the erasure error can be correctly detected, error correction up to "16B" can be carried out in one column comprising "120B". However, in a conventional technique, the erasure error is not detected, and assuming that the erasure error does not exist, correction has been carried out up to "8B" per one column. In this method, the maximum in "1" sector is correction up to "40B".
As the method of recording in the optical disk at a high density, there are the method of reducing the distance between each pit, reducing the distance between tracks, or the like. More specifically, when the method of reducing the distance between the pits is adopted, that is, when a recording linear density is increased, the distance (along the track) necessary for recording 1B is reduced.
Accordingly, comparing the optical disk having a higher linear density to the optical disk having a lower linear density, even if a scratch and dust on the former disk is the same size as those on the latter disk, there is a difference between each byte number of the error of the disks. Thereby, there is a possibility that the optical disk having the higher linear density is more disadvantageous than the optical disk having the lower linear density in view of the error correction.
In order to solve the above problem, some methods are considered. For example, a method that increases redundancy to enhance the error correction ability has been is considered. The redundancy means a ratio of the byte number all over the sector to a redundant byte number (the ECC, etc.) occupied therein. In this method, since the byte number of the ECC code is increased, the amount of the information to be recorded is increased, and there is a possibility that the effect on the high density record is reduced.
Furthermore, for example, a method using an integrated code, that is, a plurality of correction sequences are used so that the error correction ability is enhanced is also considered. When using the integrated code, an error correction code is added to each of a plurality of vertical and horizontal sequences by interleaving, and the error correction code is multiplexed. As a result, a code having a higher error correction ability can be constructed.
FIG. 15 is an ECC block diagram showing an example of a data structure using the above integrated code type correction sequence. An ECC block 55 comprises an integrated code structure in which an inner code parity PI in a horizontal direction for correcting a data error is added to an outer parity PO in a vertical direction. The ECC block 55 comprises a plurality of sectors, and sectors ID1 to IDn as address data are provided to each sector. In this method, it takes a long time to correct the data error, and sometimes, there is occurred a problem relating to data transfer rate when the information is reproduced.